In UMTS (Universal Mobile Telecommunications System) networks, for the purpose of improving spectral efficiency and further improving data rates, by adopting HSDPA (High Speed Downlink Packet Access) and HSUPA (High Speed Uplink Packet Access), it is performed exploiting maximum features of the system based on W-CDMA (Wideband Code Division Multiple Access). For the UMTS network, for the purpose of further increasing high-speed data rates, providing low delay and the like, Long Term Evolution (LTE) has been studied.
In the 3G system, a fixed band of 5 MHz is substantially used, and it is possible to achieve transmission rates of approximately maximum 2 Mbps in downlink. Meanwhile, in the LTE-scheme system, using variable bands ranging from 1.4 MHz to 20 MHz, it is possible to achieve transmission rates of maximum 300 Mbps in downlink and about 75 Mbps in uplink. Further, in the UMTS network, for the purpose of further increasing the wide-band and high speed, successor systems to LTE have been studied (for example, LTE Advanced (LTE-A)). For example, in LTE-A, it is scheduled to increase 20 MHz that is the maximum system band in LTE specifications to about 100 MHz.
Meanwhile, in the LTE-scheme system, MIMO (Multi Input Multi Output) systems are proposed as radio communication techniques for transmitting and receiving data using a plurality of antennas and improving a data rate (spectral efficiency) (for example, see Non-patent Document 1). In the MIMO systems, the transmitter/receiver is provided with a plurality of transmission/reception antennas, and simultaneously transmits different transmission information sequences from different transmission antennas. Meanwhile, the receiver side exploits the fact that different fading variations occur in between transmission and reception antennas, and divides the simultaneously-transmitted information sequences to detect, and it is thereby possible to increase the data rate (spectral efficiency).
In the LTE-scheme system, specified are Single User MIMO (SU-MIMO) transmission in which transmission information sequences simultaneously transmitted from different transmission antennas are all for the same user and Multiple User MIMO (MU-MIMO) transmission in which the transmission information sequences are for different users. In the SU-MIMO transmission and MU-MIMO transmission, the receiver side selects an optimal PMI (Precoding Matrix Indicator) from a codebook that defines a plurality of phase/amplitude control amounts (precoding matrixes (precoding weights)) to set on antennas of the transmitter and PMIs associated with the precoding matrixes, and transmits the PMI to the transmitter as feedback. The transmitter side performs precoding on each transmission antenna based on the PMI that is transmitted from the receiver as feedback, and transmits transmission information sequences. As typical precoding techniques, there are ZF (Zero Forcing), BD (Block Diagonalization) ZF, MMSE (Minimum Mean Square Error), SLNR (Signal to Leakage plus Noise Ratio), etc.
Herein, attention is directed toward SLNR precoding. In SLNR precoding, a value is maximized which is obtained by dividing power of a desired signal received in a receiver (herein, mobile terminal apparatus) by the sum of interference caused by “leakage” of a signal in another mobile terminal apparatus in the coordinated cluster, noise and all power. In calculating precoding weights by SLNR precoding, the need arises for an average reception SINR (Signal to Interference plus Noise Ratio) in the mobile terminal apparatus (for example, see Non-patent Document 2).